[WIP] Fix is_dense flag not properly set

[VictorLamoine]

Fixes #1455.

• Update documentation about what dense cloud is.
• Add some checks to make the cloud non-dense if normal, color etc.. is not finite in the PLY reader.
• Write a test for a non dense cloud.
• Fix bug with binary PLY files

test_pcl_1: /home/victor/libraries/pcl/src/io/src/ply_io.cpp:503: void pcl::PLYReader::objInfoCallback(const string&): Assertion `st.size () == 3' failed.
Abandon

[VictorLamoine]

In the PCD reader, every field has to be finite for the cloud to be dense:
https://github.com/PointCloudLibrary/pcl/blob/master/io/src/pcd_io.cpp#L989-L1038

I'll make the same for the PLY files.

[SergioRAgostinho]

Small comment to the whole NaN and Inf thing, only float and double have NaN/Inf representations. So making that check on integers is useless.

References:
http://stackoverflow.com/questions/3949457/can-an-integer-be-nan-in-c
http://stackoverflow.com/questions/8690567/setting-an-int-to-infinity-in-c

[taketwo]

Here are a few more bits of information I found about the meaning of the is_dense field. Firstly, a message from Radu that motivates the existence of the field. Unfortunately, it does not make it clear whether all fields or just XYZ need to be valid. Secondly, an example in normal estimation code where is_dense is set to false when a normal is NaN.

So I think that is_dense means that all fields of all points in a point cloud are valid. (Which, as Sergio mentioned, only makes sense for floating point representations.)

[stale]

This pull request has been automatically marked as stale because it hasn't had
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Come back whenever you have time. We look forward to your contribution.

[SergioRAgostinho]

Note to self: confirm the last point

Fix bug with binary PLY files

[VictorLamoine]

@SergioRAgostinho I don't have time to spend on PCL right now 🤕

If anyone is willing to take over my patch please do it! Don't mention me as the author or whatever, I don't care.

[stale]

This pull request has been automatically marked as stale because it hasn't had
any activity in the past 60 days. Commenting or adding a new commit to the
pull request will revert this.

Come back whenever you have time. We look forward to your contribution.